Process for producing a pipe fitting consisting of thermally weldable material

ABSTRACT

A process for producing a pipe fitting of thermally weldable material for attachment to or repair of conduits of thermally weldable material. The first injection mold has channels formed as windings and having channel walls. A heating wire is formed to a wavy heating strand which is laid into the first injection mold between the channel walls. A first welding material is introduced into the channels so that a first broad side of the wavy shape of the heating strand is pressed against a first mold surface of the injection mold and an intermediate product with embedded wavy heating strand is formed. The outside surface is formed by the first mold surface against which the heating strand is pressed and provides the contact surface with the conduit in the end product. The first broad side of the wavy shape of the heating strand remains visible at the outer surface of the intermediate product. The intermediate product is placed into a second injection mold for producing a pipe fitting so that the outer surface rests on a second mold surface of the second injection mold. A second welding material is introduced and the contact surface of the pipe fitting is formed. The first broad side of the heating strand remains visible at the contact surface after solidification of the second welding material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to a process for the production of a pipefitting, at least certain areas of which consist of thermally weldablematerial (weld material), which fitting is designed for attachment to,or for the repair of, conduits which also consist of thermally weldablematerial, wherein several windings of at least one electrical heatingwire are first laid in the desired welding area of the future contactsurface between the pipe fitting and the conduit, wherein contacts areattached, if desired, to the two ends of the heating wire laid inwindings, to which contacts an electrical power source is connectedduring the later welding of the pipe fitting, and then the position ofthe windings of the heating wire and possibly the position of thecontacts are fixed by welding material which is applied in theinjection-molding process. Pipe fittings are used for various purposesto be mounted on a previously installed conduit for media such as gas orwater, possibly while the conduit is under the pressure of the medium.Appropriate pipe fittings are also used for repair purposes or toconnect sections of pipe. At least certain areas of the pipe fitting andof the conduit consist of thermoplastic resin. In these cases, the pipefitting has a welding area at its contact surface with the conduit,where several windings of at least one electric heating wire are laid.Contacts which serve to connect the wire to a source of electric powerwhen the pipe fitting is welded on at a later time are usually attachedto the ends of the heating wire.

2. Description of the Related Art

In the known process, windings of a heating wire of the type in questioncan be laid directly in the injection mold used to produce the pipefitting; this wire is thus integrated into the welding material of thepipe fitting during the injection-molding process (CH 528,697 C). Theheating wire is surrounded by a plastic jacket, which hinders the flowof heat to the contact surface between the pipe fitting and the conduit.The windings of the heating wire can be laid in the mold as a monofilaror bifilar spiral or as a meander.

It is also known that a plate-shaped intermediate product can beproduced out of the heating wire. This is done by winding the heatingwire into a bifilar spiral and by connecting these spiral windings toeach other by plastic webs (DE 3,810,845 A1). Finally, it is also knownthat the heating wire can first be brought into the form of a helix, andthat the helix can then be embedded in a star-shaped intermediateproduct of thermoplastic material (DE 7,121,715 U). When the pipefitting is injection-molded, this star-shaped intermediate product isthen integrated into the area of the contact surface with the conduit.The current flowing through the helix leads to maximum heating in theinterior of the helix, however, and this beat is therefore unavailablefor the welding process with the conduit. The heat which reaches thecontact surface is inadequate. In these known pipe fittings, thestrength of the weld to the conduit is unreliable. To achievesatisfactory welding results, it is necessary to use a relatively largeamount of electrical energy, which is uneconomical.

SUMMARY OF THE INVENTION

The invention is based on the task of providing an economical processfor producing pipe fittings of the aforementioned kind, the end productsof which can be welded quickly and reliably to conduits. This isachieved according to the invention in that the heating wire, or atleast certain sections thereof, is formed into a flat, wavy shape, as aresult of which a wavy heating strand is produced as a first step; inthat only then are the windings of the wavy heating strand laid in thefuture welding area of the pipe fitting; wherein, after theinjection-molding of the pipe fitting and the solidification of thewelding material, one of the broad sides of the wavy shape extends alongthe contact surface.

The process according to the invention proceeds in two stages. First,the heating wire is brought into the form of a flat, wavy line, as aresult of which a special intermediate product is obtained, which is tobe referred to below in brief as the “heating strand”. The specialfeature of this heating strand is therefore to be found in its wavyshape, which can also be described as a sine wave. Then, in the secondstage of the process, windings of this wavy heating strand are laid inthe injection mold in such a way that one of the broad sides of its wavyshape lies directly at the contact surface with the pipe fitting. Thewavy shape and its position at the surface ensure the rapid, intenseheating of the contact surface even when only a moderate amount ofcurrent flows through the strand. The softening and coalescence of thematerial of the pipe fitting and the conduit lead to a reliable weldafter solidification.

Additional measures and advantages of the invention can be derived fromthe subclaims, from the following description, and from the drawings.The invention is intended to cover all of the novel features andcombinations of features which can be derived from them, even if theseare not explicitly stated in the claims. The invention is illustrated inthe form of an exemplary embodiment in the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a top view of an intermediate product for a pipe fittingproduced in accordance with the invention;

FIG. 2 shows a schematic cross section of the intermediate product ofFIG. 1;

FIG. 3 shows, on an enlarged scale, a bottom view of part of theintermediate product shown in FIG. 1;

FIG. 4 shows, at the same degree of enlargement, a top view of the partof the intermediate product shown in FIG. 3;

FIG. 5 shows a cross section through the part of the intermediateproduct shown in FIG. 4 along line V—V of FIG. 4;

FIG. 6 shows a schematic diagram of several components of a device whichis used to give the heating wire a wavy shape, as a result of which awavy heating strand is obtained;

FIG. 7 shows a perspective view, on an enlarged scale, of part of thewavy heating strand of FIG. 6, which is integrated into the intermediateproduct of FIGS. 1-5;

FIGS. 8 and 9 show schematic diagrams of parts of an injection mold forthe production of the intermediate product shown in FIGS. 1-5, in twodifferent working stages;

FIG. 10 shows a schematic diagram of a cross section through anadditional injection molding device, which holds the intermediateproduct of FIGS. 1-5 and is used to produce a pipe fitting;

FIG. 11 shows, on an enlarged scale, a part of the device shown in FIG.10;

FIG. 12 shows a cross section through a part of the pipe fitting whichcan be produced in the device of FIG. 10, the position of this endproduct while in service on a conduit also being indicated;

FIG. 13 shows a side view of a different exemplary embodiment of aintermediate product similar to that of FIG. 1;

FIG. 14 shows a cross-sectional view of the intermediate product of FIG.13 along III—III; and

FIG. 15 shows a side view of the end product made from the intermediateproduct of FIGS. 13 and 14, the figure also showing how the end productis used to join two sections of conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The goal of the invention to produce a pipe fitting 50 such as thatshown by way of example in FIG. 12, at least certain areas of whichconsist of a weldable material 51, namely, a thermoplastic material,such fittings being designed to be welded to a desired location on aconduit 56, which also consist of a thermally weldable material. Thismaterial is to be referred to below in brief as “welding material”. Toachieve its purpose, pipe fitting 50 has a saddle 53, which, in themounted state, comes into contact by its contact surface, designated 54,with conduit 56. To produce the weld, a heating wire 10, to be describedin greater detail further below, is integrated into a certain weldingarea 55. This heating wire 10 is first given a special shape, to bepresented in greater detail below, and is a component of a specialintermediate product 20, which is shown in FIGS. 1-5. During theinjection-molding of pipe fitting 50, this intermediate product 20 isintegrated into the desired welding area 55, as can be seen in FIG. 12.A pipe fitting of this type can have one or more pipe sockets 52. Afterthe pipe fitting has been welded in place, socket 52 offers access toconduit 56 so that a hole can be drilled through it at the spotindicated by reference number 57.

As shown in FIG. 6, the starting point is a bare heating wire 10, whichdoes not have any insulating jacket but which does have sections 12,which have been brought into the form of a flat, wavy line 11. Heatingwire 10 has at most a conventional, minimal enamel finish. There can bestraight sections 13 of wire between wavy sections 12. This wavyintermediate product 15 is shown in perspective in FIG. 7 and isreferred to in brief in the following as the “heating strand”. The wavyshape 11 of heating strand 15 is produced by conducting the originallystraight wire, as can be seen in FIG. 6, between two intermeshing gearwheels 14. Gear wheels 14 have a toothed pro file in the form of thesame wavy shape 11. In the present case, the wavy shape is in the formof a sine wave. Straight sections 13 of wire between wavy sections 12are produced by moving the two gear wheels 14 away from each other whilesection 13 is passing between them in the direction of the arrow in FIG.6. Thus the teeth of gear wheels 14 are no longer able to deform heatingwire 10.

An injection mold with two mold halves 31, 32 is used to produceintermediate product 20. FIGS. 8 and 9 show enlarged cross sections ofthis mold. Whereas mold half 31 is designed as an essentially flatplate, the other half 32 of the mold has a channel 33, which is designedhere as a flat, monofilar spiral. Channel 33 can be divided into twopartial cross sections 30, 34, which serve different functions. One part30 of the cross section has the form of a trapezoid, the largertrapezoidal side being open toward the other half 31 of the mold. Thispartial cross section 30 serves to accept wavy heating strand 15. Thechannel walls of this partial cross section 30 are undercut and gripopposing peaks 16 of heating strand 15, as can be seen in FIG. 7.Inserted heating strand 15 has a certain transverse elasticity and isheld in place in partial cross section 30 even while the two halves 31,32 of the mold are open. In correspondence with the pattern of thewindings of channel 33, heating strand 15 itself assumes the form ofspiral windings 70 according to FIG. 3.

A flow cross section 34 in the form of a semicircular arc, which liesabove the previously mentioned, trapezoidal partial cross section 30,also belongs to channel 33. After the injection mold has been closed,this partial cross section serves according to FIG. 9 to guide the flowof welding material 21, illustrated by the arrows. When intermediateproduct 20 is being made, welding material 21 flows toward theupward-facing, broad side 18 of heating strand 15, as a result of whichheating strand 15 is pressed against mold surface 37 of adjacent half 31of the mold. After welding material 21 has solidified in injection mold31, 32, therefore, intermediate product 20 shown in FIGS. 1-5 isobtained. FIG. 3 shows a bottom view, where wavy shape 11 remainsvisible on outside surface 27. At the same time, the wavy shape ensuresthat heating strand 15 is firmly anchored in the welding material ofintermediate product 20, which also has the following additional specialdesign feature.

After the plastic material has solidified, a band 23 with thecorresponding pattern of windings is formed in the individual spiralturns of channel 33. Width 19 of the wavy shape visible in FIG. 7 isessentially the same as width 39 of the channel used to produce theband, which can be seen in FIG. 9. Therefore, wavy shape 11 passingaround individual turns 70 of band 23, as shown in FIG. 3, extends allthe way across width 29 of the band, proceeding from one edge of theband to the other. This is also easy to see in the cross section shownin FIG. 5.

As illustrated in FIG. 9, the individual windings of channel 33 are acertain radial distance 35 away from each other, for which reason opengaps 25 are formed in intermediate product 20 between individualwindings 23 of the band. These gaps 25 are bridged in intermediateproduct 20 by connecting ribs 24, as shown in FIG. 1. These connectingribs 24 are formed by distribution lines, not shown in detail, providedin injection mold 31, 32; these lines proceed from a central gate 44shown in FIG. 1 and extend essentially in the radial direction acrossintermediate product 20, which here is in the form of a circular disk.These distribution lines conduct welding material 21 from gate 44 to theindividual windings 33 of the channel and ensure that the masses flowprimarily into the described flow cross sections 34, which have arounded profile, which is offset with respect to the cornered profile ofreceptacle cross sections 30. In the finished band 23, curved,longitudinal beads 43, which are visible in FIG. 4, are thus formed inthe area of these flow cross sections 34. As can be seen from completedintermediate product 20 in FIG. 5, the cross section of the distributionline which produces connecting rib 24 is taller than channel 33 servingto produce band 23, for which reason connecting ribs 24 project beyondinside surface 28 of intermediate product 20 visible in FIG. 1 andextend without a break. Connecting ribs 24, which are of uniform width,have an arc-like curvature, which is favorable for the flow of material.

Intermediate product 20, finally, also has radial, transverse webs 36,which project beyond the circular outline of intermediate product 20.These are formed by appropriately designed transverse chambers (notshown) in injection mold 31, 32, which terminate in expanded chamberareas (not shown). Previously mentioned straight wire sections 13 arelaid in these transverse chambers up as far as the chamber expansionswhen heating strand 15 is laid in the mold, as can be derived from FIGS.3-5. At the same time, contacts 40 are also laid in the chamberexpansions, so that, after the injection and solidification of weldingmaterial 21, cups 46, visible in FIGS. 1 and 2, are formed at end oftransverse webs 36 to hold contacts 40. As can be derived from FIG. 5,straight wire sections 13 pass at a sufficiently high level 38 abovewavy heating strand 15; this applies especially to straight section 13of long transverse web 36, which proceeds from the wavy section of theheating wire of innermost winding 23′ of the band shown in FIG. 1.Straight wire section 13 can, as shown in the figure, extend either inthe interior of transverse web 36 or on the top surface of this web 36.

In the completed intermediate product, according to FIGS. 1-5, theposition of flat wavy shape 11 of heating strand 15 and the position ofcontacts 40 are established by welding material 21. This intermediateproduct thus serves as a carrier for the windings of special heatingstrand 15 and can therefore be described below as the “heating strandcarrier”. In the flow direction indicated by the arrows in FIG. 1, aflat, in this case ring-shaped, boundary zone 18 is provided inside ofinner most winding 23′ of the band, based on gate 44 as the center; thiszone is formed by a appropriate starting chamber (not shown) ininjection mold 31, 32. This starting chamber is supplied with weldingmaterial via the previously mentioned distribution lines, which serve toform connecting ribs 24 in heating strand carrier 20. This cross sectionof this chamber is flatter than overall cross section 34, 30 of channels33 serving to produce band 23. This is significant for the furtherprocessing of heating strand carrier 20 according to the invention inpipe fitting 50 to be obtained, as can be seen on the basis of FIGS. 10and 11. Central part 49 in FIGS. 1 and 2 is cut out so that flatboundary zone 18 with its circular opening 22 begins there. In thepresent case, heating strand carrier 20 is a flat, level product.Because of open gaps 25 remaining between windings 23 of the band andconnecting ribs 24, heating strand carnier 20 has the character of amat; it is flexible, and its original flat contour shown in FIGS. 1 and2 can be easily deformed into a cylinder. This is significant for thefollowing stages of the processing of heating strand carrier 20.

To produce pipe fitting 50, a second injection mold 41, 42 shown inFIGS. 10 and 11, is used. It consists of a mold half 41 on the nozzleside, with a nozzle 45 for the introduction of the previously mentionedwelding material 51, and a mold half 42 on the ejector side, serving toeject finished pipe fitting 50. The previously produced heating strandcarrier 20 of FIGS. 1-5 is first inserted into ejector-side mold half 42after the injection mold has been opened. Suitable receptacles forprojecting contacts 40, previously mentioned, are also provided there.When injection mold 41, 42 is brought into the closed position shown inFIGS. 10 and 11, central circular opening 22 of heating strand carrier20 is automatically set down onto a nozzle bush 48 of opposite mold half41, This nozzle bush 48 surrounds central nozzle 45, which supplies theflow of material, and rises above prominent saddle-shaped mold surface47 of mold half 41. When, as FIG. 11 shows, welding material 51 flows inthe direction of the arrows into the cavity between the two mold halves41, 42, it first arrives at the side of flat boundary zone 71 of heatingstrand carrier 20 facing away from mold surface 47 and presses outsidesurface 27 of the boundary zone against saddle-shaped mold surface 47 ofmold half 41. The originally flat mat of heating strand carrier 20 istherefore deformed on this saddle surface 47 into a partial cylinder. Itis therefore impossible for incoming welding material 51 to pass intocircular opening 22 between nozzle bush 48 and flat boundary zone 71 andarrive at outside surface 27 of heating strand carrier 20.

The two mold halves 41, 42 have suitable coolant channels 58 to ensurethe rapid solidification of injected welding material 51. After the moldhas been opened, it is then possible in the present case to removepreviously described end product 50, shown in FIG. 12, by means of asuitable ejector (not shown) from mold half 42. Previously mentionedmold surface 47 of nozzle-side mold half 41 produces previouslymentioned contact surface 54 on end product 50. In this area, integratedheating strand carrier 20 with its described outside surface 27 remainsfree of welding material 51, because this material is able to flow onlyinto remaining gaps 25, which it then closes. The entire outward-facingbroad side 17 of heating strand 15, in the form of a wavy line,therefore remains with visible. It would also be possible to use adifferent injection mold in which heating strand carrier 20 would beformed into a complete cylinder.

It is therefore guaranteed that outward-facing, broad side 17 of wavyshape 11 remains visible on outside surface 27 of intermediate product20 and thus also at contact surface 54 of end product 50. In practice,wavy shapes 11 actually project slightly beyond outside surface 27,which can be explained by the shrinkage of welding material 51. Exposedwavy shape 11 is very effective at increasing the efficiency of thelater welding operation by which pipe fitting 50 is attached to conduit56. Electrical insulation problems cannot arise, because the lateralsurface of conduit 56 to be welded also consists of electricallynonconductive, thermoplastic material.

FIGS. 13 and 14 show a different exemplary embodiment of a heatingstrand carrier 20′ according to the invention. Elements analogous tothose of mat-like heating strand carrier 20 of the preceding exemplaryembodiment are designated here by the same reference numbers, for whichreason the previous description also applies here to that same extent.It is sufficient to describe only the differences.

One difference consists in that band windings 23 provided here are inthe form of a helix from the very beginning and therefore present acompletely cylindrical form right in intermediate product 20′ itself, asis especially easy to see in FIG. 14. What cannot be seen in FIGS. 13and 14, is that, of course, the wavy heating strand extends along theseband windings 23 in the previously described manner. Individual windings23 of the band are joined here, too, by connecting ribs 24, which,however, can also be parallel to the axis of the cylinder. This designis presented in the form of two axial cross sections 59 of intermediateproduct 20′ , which has the form of a cylindrical basket.

Cylindrical basket 20′ thus obtained serves to produce end product 60,shown in a side view in FIG. 15. End product 60 represents in this casea connecting sleeve 60, which is used to connect the ends of two pipes61, 62 together. During the injection-molding of this connecting sleeve60, cylindrical basket 20′ comes to rest on inside sleeve surface 63illustrated in FIG. 15, where, in the manner already described in thepreceding case, one of the broads side of the wavy shape rests isexposed on the inside 64 of the sleeve. Heating strand 15 used in thepresent case has three of the straight wire sections 13 explained inconjunction with FIG. 6, two of which, as in the preceding case, serveto connect contacts 40, provided here at the ends of cylindrical basket20′, but which are not visible in FIG. 13. The third wire section 13 islocated between the above-mentioned axial sections 59 and is shown inFIG. 13. Here there is a central ring 65, which is produced out ofwelding material 21 of cylindrical basket 20′ and which, in the case ofend product 60 of FIG. 15, ends up in the center 66 of the sleevebetween the two end surfaces of pipes 61, 62 to be connected.

When FIG. 15 is in service, an inside stop 67, which fixes the positionof pipes 61, 62 in the interior of the sleeve, is located between thetwo end surfaces of pipes 61, 62. This stop 67 could be produced bywelding material 21 of cylindrical basket 20′. But it is also possiblefor stop 67 to be formed later on out of the welding material ofconnecting sleeve 60, by providing an appropriate opening in centralring 65 and by designed the injection mold for connecting sleeve 60 in acorresponding manner. This opening in central ring 65 is filled up bythe welding material of connecting sleeve 60, with the result thatinside stop 67 is formed in the interior of the sleeve. Gaps 25 betweenbands 23 extending around the helix, however, are filled up flush by thewelding material of connecting sleeve 60, so that here, too, the wavylines in tapes 23 remain exposed in interior 64 of the sleeve. Contacts40 of cylindrical basket 20′ in FIG. 13 end up in plastic shoulders 69of finished connecting sleeve 60 of FIG. 15.

A wavy heating strand 15 could also be used to produce a mat-likeintermediate product, which later forms a contact surface of a so-calledmulti-shell “muff”, the shells of which form a complete cylinder whichenclose the conduit. In the production of an end product of this type,at least some areas the intermediate product mats used here are formedinto more than half-cylinders in the injection mold. The special patternof the windings of the band in a mat such as this is illustrated inGerman patent Application No. 196-23,353.4.

List of Reference Numbers

10 heating wire

11 wavy shape

12 wavy section of 15

13 straight section of 15

14 gear wheels for 15

15 heating strand

16 peak area of 11

17 outward-facing broad side of 11

18 inward-facing broad side of 11

19 width of wavy shape 11

20 intermediate product, mat-like heating strand carrier

20′ intermediate product, cylindrical basket

21 welding material of 20

22 circular opening in 20 at 18

23 band, windings of the band

23′ innermost windings of the band on 20

24 connecting rib between 23, 23′

25 open gap between 23

26 longitudinal corner of band 23

27 outside surface of 20 and 25

28 inside surface of 20

29 width of band

30 partial cross section of 33, receptacle cross section for 15

31 injection mold for 20, first half

32 injection mold for 20, second half

33 channel in 32, channel winding

34 partial cross section of 33, flow cross section

35 distance between 33

36 transverse web of 20

37 mold surface in 31

38 differences in height between 13 and 15

39 channel width of 33

40 contact

41 injection mold for 50, mold half on the nozzle side

42 injection mold for 50, mold half on the ejector side

43 longitudinal bead on 23

44 gate for 24 on 20

45 nozzle on 41

46 cup for 40 (FIGS. 1, 2)

47 saddle-shaped mold surface of 41

48 nozzle bush on 45

49 central part of 20

50 pipe fitting, final product

51 welding material for 50

52 pipe socket on 50

53 saddle of 50

54 contact surface on 53

55 welding area of 50 to 53

56 conduit for 50

57 drilling point for 50 to 56

58 coolant channel in 41, 42

59 axial section of 20′, with openings

60 connecting sleeve, pipe fitting, end product

61 first pipe

62 second pipe

63 inside surface of sleeve

64 interior of sleeve of 20′

65 ring of 20′ for 13

66 middle of sleeve 60

67 inside stop in 64

68 end ring of 20′

69 shoulder for 40 (FIG. 15)

70 winding of 15 (FIG. 3)

71 flat boundary zone of 20

What is claimed is:
 1. A process for producing in an injection mold apipe fitting having at least some areas consisting of thermally weldablewelding material, the pipe fitting configured to be attached to or toconnect or repair conduits consisting of thermally weldable material,the method comprising the steps of: providing channels formed aswindings and provided with channel walls in a first injection mold;giving a wavy shape to at least some sections of a heating wire so as toform a wavy heating strand; laying the wavy heating strand into thefirst injection mold between the channel walls of the channels;introducing a first welding material into the channels so that a firstbroad side of the wavy shape of the heating strand is pressed against afirst mold surface of the injection mold, and producing an intermediateproduct having the wavy heating strand embedded in the intermediateproduct and having an outside surface which, in the pipe fitting, willform the contact surface with a conduit, wherein the outside surface isformed by the first mold surface against which the heating strand ispressed and wherein the first broad side of the wavy shape of theheating strand remains visible at the outer surface of the intermediateproduct; placing the intermediate product into a second injection moldconfigured to produce the pipe fitting and positioning the outer surfaceon a second mold surface of the second injection mold; introducing asecond welding material into the second injection mold for molding thepipe fitting and forming on the second mold surface the contact surfaceof the pipe fitting for contacting the conduits, wherein the first broadside of the wavy shape of the heating strand remains visible at thecontact surface of the end product after solidification of the secondwelding material.
 2. The process according to claim 1, wherein thechannel walls of the channel of the first injection mold are undercut,wherein the heating strand laid in the channel has a certain transverseelasticity, and wherein opposite peak areas of the wavy shape pressagainst the undercut channel walls.
 3. The process according to claim 1,wherein, in the step of introducing the first welding material into thefirst injection mold, the welding material is conducted essentiallyagainst a second broad side of the wavy shape of the heating strandfacing an interior of the channels and the first broad side of the wavyshape of the heating strand is pressed by the flow of the weldingmaterial against the first mold surface.
 4. The process according toclaim 1, wherein the windings of the channels are spaced at a radialdistance from one another and the intermediate product is formed in thewindings of the channels as a band with adjacent windings having opengaps between the adjacent windings of the band.
 5. The process accordingto claim 4, wherein the wavy shape of the heating strand has a wavinesswith a width essentially equal to a width of the channels in theinjection mold, wherein, in the step of introducing the first weldingmaterial, the outer broad side of the wavy shape of the heating strandis pressed toward the outer side of the band and extends over the entirewidth of the band from one edge of the band to the opposite edge of theband.
 6. The process according to claim 4, wherein the channels, incross section, are divided into two partial cross sections, wherein afirst one of the cross sections is an undercut receptacle for the wavyheating strand and is positioned proximal to the first mold surface andacts on opposite peak areas of the wavy shape of the heating strand, anda second one of the cross sections is a flow cross section forconducting a flow of the first welding material, wherein the secondcross-section is positioned remote from the first mold surface.
 7. Theprocess according to claim 4, wherein the radial distance between thewindings of the channels are bridged by one or more distribution lines,wherein at least some of the first welding material flows first into theone or more distribution lines and proceeds from the one or moredistribution lines into the individual windings of the channels, whereinthe first welding material solidifies in the one or more distributionlines and forms connecting ribs connecting the windings of the band. 8.The process according to claim 7, wherein the distribution lines have aconducting cross section which is taller than a flow cross section ofthe channels, and wherein, after the introduction and solidification ofthe first welding material in the distribution lines, the connectingribs are formed continuously across the windings of the band on aninside surface of the intermediate product opposite the outer surface.9. The process according to claim 8, wherein the distribution lines andthe connecting ribs are arc-shaped.
 10. The process according to claim4, wherein, in the step of. introducing the first welding material intothe first injection mold, the first welding material is introducedthrough a gate and wherein the distribution lines extend away from thegate.
 11. The process according to claim 4, wherein, in the step ofgiving a wavy shape to at least some sections of the heating wire,intermediate sections are left undeformed between the sections of thewavy shape and the intermediate sections are straight wire sections,wherein the first injection mold has transverse chambers extending abovethe windings of the channels and provided with terminal chamberexpansions, wherein, before the step of introducing the first weldingmaterial, the straight wire sections are laid in the transverse chambersso as to cross over the wavy sections of the heating strand at avertical distance, wherein the free ends of the straight wire sectionshaving associated contacts are laid into the terminal chamberexpansions, and wherein the first welding material flows into thetransverse chambers and the terminal chamber expansions to form atransverse web with a terminal contact after solidification of the firstwelding material.
 12. The process according to claim 11, wherein thetransverse chambers have a chamber cross section rising above the crosssection of the distribution lines, and wherein the transverse websproduced after solidification of the first welding material on the innersurface of the intermediate product are higher than the connecting ribs.13. The process according to claim 2, wherein, seen in the flowdirection of the first welding material, a starting chamber is providedin the first injection mold upstream of a first one of the windings ofthe channel, wherein the cross section of the starting chamber isflatter than the cross section of the channels, wherein, aftersolidification of the first welding material in the starting chamber, aflat boundary zone is produced on the intermediate product which issituated before a first winding of the band.
 14. The process accordingto claim 13, wherein a first mold half of the second injection mold hasa nozzle surrounded by a nozzle bush and configured to introduce thesecond welding material, wherein the flat boundary zone of theintermediate product is set down onto the nozzle bush such that theinside surface of the intermediate product faces an opening in thenozzle, wherein a flow of the second welding material arrives first atthe flat boundary zone of the intermediate product and thereafter flowsinto adjacent windings of the-band and causes the outer surface of theintermediate product to be pressed against the second mold surface ofthe second injection mold provided on the first mold half.
 15. Theprocess according to claim 14, wherein the intermediate product is laidinto the second mold half of the second injection mold opposite thefirst mold half, the second mold half being used to eject the finishedpipe fitting (50), and is automatically pushed onto the nozzle bush ofthe first mold half when the first and second mold halves of the secondinjection mold are closed.
 16. The process according to claim 4, whereinthe intermediate product is a heating strand carrier formed as a flatmat and wherein the band in which the wavy heating strand is received islaid out as windings of a monofilar or bifilar spiral.
 17. The processaccording to claim 16, wherein the mat is formed into a partial orcomplete cylinder in the second injection mold.
 18. The processaccording to claim 16, wherein the mat is a circular disk.
 19. Theprocess according to claim 1, wherein the intermediate product is formedin the windings of the channels as a band with adjacent windings,wherein the intermediate product is a heating strand carrier in the formof a cylinder, wherein at least some of the windings of the band form ahelix and a cylindrical basket, wherein the cylindrical basket is formedin the second injection mold to a pipe collar or a pipe-connecting orrepair sleeve with an inside surface, wherein the first broad side ofthe wavy shape of the heating strand is freely exposed.